And, IIRC, also against NFL policy which requires teams to be on the field for the anthem.
Prior to 2008 the teams were never on the field for the Anthem, always in the locker room. Not sure what changed in 2008. Teams have not always been on the field for the Anthem.
If so then apparently NFL rules are merely....suggestions. Players and teams can do whatever whims might amuse them each game day. Gansta symbols on helmets...etc. Maybe gangs will sponsor some players and they can make up lost revenue that way (like stadium naming rights)?